1. Field of the Invention
The present invention relates to an image blur prevention apparatus for preventing an image from being blurred by moving a movable member.
2. Description of the Related Art
Camcorders having a function for preventing image blur resulting from camera shake during photographing have recently become commercialized, and also research and development for still cameras having an image blur prevention function is under way.
As an image blur prevention apparatus for preventing an image from being blurred even if the camera is shaken during photographing, apparatuses utilizing various methods have already been proposed. An example of a known optical apparatus having a shake prevention apparatus proposed by the applicant of the present invention will be explained below with reference to FIG. 14. FIG. 14 is a schematic view of a lens barrel having a shake prevention apparatus proposed by the applicant of the present invention, also schematically illustrating the shake prevention apparatus.
Referring to FIG. 14, reference numeral 82 denotes an outer barrel of the lens barrel; reference numeral 84 denotes an inner barrel which is housed in the outer barrel 82; reference numeral 83p denotes an angular displacement detecting means, mounted on the outer peripheral surface of the inner barrel 84, for detecting the angular displacement of the longitudinal shake (pitching) P of the lens barrel; reference numeral 83y denotes an angular displacement detecting means, mounted on the outer peripheral surface of the inner barrel 84, for detecting the angular displacement of the lateral shake (yawing) Y of the lens barrel; reference numeral 80 denotes a correction lens for preventing image blur on the surface of a film 88 even if the lens barrel is shaken; reference numeral 81 denotes a correction lens holding frame for holding the correction lens 80, disposed so as to face the end surface in the back portion of the inner barrel 84 in such a manner as to be movable vertically and from side to side; reference numeral 86p denotes a coil, mounted in the holding frame 81, which constitutes a part of first electromagnetic driving means for causing the holding frame 81 to move vertically; reference numeral 86y denotes a coil, mounted in the holding frame 81, which constitutes a part of second electromagnetic driving means for causing the holding frame 81 to move from side to side; reference numeral 87p denotes a longitudinal position detecting means for detecting the position when the holding frame 81 is moved vertically by the first electromagnetic driving means and the amount of the movement of the holding frame 81; reference numeral 87y denotes a lateral position detecting means for detecting the position when the holding frame 81 is moved from side to side by the second electromagnetic driving means and the amount of the movement of the holding frame 81; and reference numeral 89 denotes a cover for covering the holding frame 81 and the like.
The angular displacement detecting means 83p and 83y are formed of detecting means formed of a known vibration gyroscope or the like and an integration circuit. The longitudinal position detecting means 87p and 87y for detecting the positional change of the holding frame 81 are formed of a light projection element formed of an infrared emitting diode and a photoreceptor element formed of a known position sensing device (PSD). The output of the angular displacement detecting means 83p and 83y and the signals output from the correction lens position detecting means (PSD) are input to a control circuit (not shown) whereby predetermined processing is performed, after which two electromagnetic driving means, including the coils 86p and 86y, are driven in accordance with the signals output from the control circuit in order to control the position and driving of the correction lens 80. Hereinafter the component member formed of the correction lens 80 and the holding frame 81 will be described as correction optical means 85.
Next, specific construction examples of the lens barrel explained in FIG. 14 will be explained with reference to FIGS. 15 to 17. FIGS. 15 and 16 are exploded perspective views of another lens barrel having nearly the same construction as the lens barrel explained in FIG. 14 viewed from the film surface side, i.e., from behind in FIG. 14. In FIGS. 15 and 16, however, the outer barrel 82 and the angular displacement detecting means 83p and 83y of FIG. 14 are not shown. A specific example of the control circuit which is not depicted in FIG. 14 is shown in FIGS. 16 and 17.
Since the reference numerals used in FIG. 14 are different from those used in FIGS. 15 to 17, before an explanation of FIGS. 15 to 17 is given, the correspondence between the components designated by the reference numerals in FIG. 14 and the components designated by the reference numerals in FIGS. 15 to 17 will be explained.
In FIGS. 15 to 17, reference numeral 710 denotes a lens barrel corresponding to the inner barrel 84 shown in FIG. 14; reference numeral 71 denotes a correction lens corresponding to the correction lens 80 shown in FIG. 14; reference numeral 72 denotes a correction lens holding frame corresponding to the correction lens holding frame 81. A coil 79p mounted in the lens holding frame 72 is a coil corresponding to the coil 86p of FIG. 14; a coil 79y mounted in the lens holding frame 72 is a coil corresponding to the coil 86y of FIG. 14; the two light projecting elements 76p and 76y mounted at two places of the lens holding frame 72 are in a pair with two position detecting elements 78p and 78y, such as PSDS, mounted in the lens barrel 710, and are position detecting means corresponding to the position detecting elements 78p and 78y of FIG. 14; and reference numeral 724 denotes a cover corresponding to the cover 89.
Since, as described above, the correspondence between the construction shown in FIGS. 15 and 16 and the construction explained in FIG. 14 has become clear, a specific example of the prior art proposed by the applicant of the present invention, shown in FIGS. 15 to 17, will be explained below.
Referring to FIGS. 15 and 16, reference numeral 91 denotes a magnetic pole unit which, together with the coil 79p, constitutes electromagnetic driving means along the vertical direction, which unit is placed in a recess portion 710pb on the back end surface of the lens barrel 710, and a yoke 712p.sub.3 which will be described later is inserted into the coil 79p and fixed to the lens barrel 710. A magnetic pole unit 92 constitutes electromagnetic driving means along the lateral direction, which unit is placed in a recess portion 710yb on the back end surface of the lens barrel 710, and a yoke 712y3 is inserted into the coil 79y and fixed to the lens barrel 710.
The magnetic pole units 91 and 92 each are formed by making two magnets sandwiched between three yokes. In the pole unit 91, two magnets 713p are sandwiched and held between three yokes 712p.sub.1 to 712p.sub.3. In the pole unit 92, two magnets 713y are sandwiched and held between three yokes 712y.sub.1 to 712y.sub.3.
The lens holding frame 72 is supported by a support arm 75 shown in FIG. 15 so as to be able to move vertically and from side to side. The support arm 75 is mounted in a claw portion 710a on the back end surface of the lens barrel 710.
Reference numeral 93 denotes a lock/unlock apparatus (locking means) for prohibiting and releasing the movement of the lens holding frame 72, which lock/unlock apparatus has a solenoid 719 for locking and unlocking the holding frame 72 and a spring 720 for maintaining the unlocked state. The lock/unlock apparatus 93 is disposed so as to face the lower portion on the back end side of the lens holding frame 72 and is fixed to the back end surface of the lens barrel 710 by means of screws.
A correction optical means drive control circuit 94 (FIG. 16) for driving and controlling coils 79p and 79y of the electromagnetic driving means are connected to the coils 79p and 79y, and connected to the position detecting elements 78p and 78y, such as PSDs, which are position detection signal output means for the lens holding frame 72, and are also connected to a camera control circuit (not shown) and a lens barrel control circuit (not shown).
As shown in FIG. 15, a bearing 73y is press-fitted to the lens holding frame 72, and a support shaft 74y is supported so as to slide axially by the bearing 73y. A recess portion 74ya of the support shaft 74y is engaged with a claw 75a of the support arm 75 shown in FIG. 15. Also, as shown in FIG. 15, a bearing 73p is press-fitted to the support arm 75, so that a support shaft 74p is supported so as to slide axially.
Light projection elements 76p and 76y, such as IRED-LEDs, are bonded to light-projection device mounting holes 72pa and 72ya of the lens holding frame 72, respectively, and the terminals of the light projecting elements 76p and 76y are soldered to lids 77p and 77y, respectively, which serve also as connection substrates. The lids 77p and 77y are bonded to the lens holding frame 72. The slits 72pa and 72yb are disposed in the lens holding frame 72, and the light emitted from the light projection elements 76p and 76y enters the position detecting elements 78p and 78y through the slits 72pa and 72yb, respectively. The coils 79p and 79y are also connected to the lens holding frame 72, and the terminals of the coils are soldered to the lids 77p and 77y.
Three support balls 711 are inserted into the lens barrel 710, and a recess portion 74pa of the support shaft 74p is engaged with the claw portion 710a of the lens barrel 710.
The yokes 712p.sub.1, 712p.sub.2 and 712p.sub.3, and the magnet 713p are bonded to each other and stacked on each other, and the yokes 712y.sub.1, 712y.sub.2 and 712y.sub.3, and the magnet 713y are bonded to each other and stacked on each other as well. The poles of the magnets are as indicated by the arrows 713pa and 713ya. The yokes 712p.sub.2 and 712y.sub.2 are screwed to the recess portions 710pb and 710yb of the lens barrel 710, respectively.
The position detecting elements 78p and 78y, such as PSDs, are bonded to sensor seats 714p and 714y (714y is not shown), respectively, the position detecting elements 78p and 78y are covered with sensor masks 715p and 715y, and the terminals of the position detecting elements 78p and 78y are soldered to a flexible printed circuit board 716. Dowels 714pa and 714ya (714ya is not shown) of the sensor seats 714p and 714y are inserted into mounting holes 710pc and 710yc of the lens barrel 710, and the flexible printed circuit board 716 is screwed to the lens barrel 710 by a flexible printed circuit board stay 717. Ears 716pa and 716ya of the flexible printed circuit board 716 pass through holes 710pd and 710yd and are screwed to the yokes 712p.sub.1 and 712y.sub.1, respectively. The coil terminals and the light projection device terminals on the coil terminal lids 77p and 77y are respectively connected to the ears 716pa and 716ya of the flexible printed board 716 and the land portion 716b through polyurethane copper wires (three twisted wires).
The solenoid 719 is screwed to a chassis 718 of locking means 93. One end of the solenoid 719 is inserted into a lock arm 721 charged by a spring 720, and the lock arm 721 is rotatably screwed to the chassis 718 by means of a shaft screw 722. The chassis 718 of the locking means 93 is screwed to the lens barrel 710, and the terminal of the solenoid 719 is soldered to the land 716b of the flexible printed board 716.
Three adjustment screws 723 whose tips are formed in a spherical shape (FIG. 16) are screwed through the chassis 718 of a yoke 712p and the locking means 93, and the adjustment screws 723 and support balls 711 sandwich the sliding surface (the shaded portion 72c in FIG. 15) of the lens holding frame 72. The adjustment screws 723 are adjusted in screwing so as to face the sliding surface 72c with a slight clearance in between. The cover 724 is bonded to the lens barrel 710 and covers the above-described correction optical means.
In the correction optical means drive control circuit 94 shown in FIG. 16, when the output from the position detecting elements 78p and 78y is amplified by amplifier circuits 727p and 727y and input to the coils 79p and 79y, the lens holding frame 72 is driven vertically or from side to side, and the output of the position detecting elements 78p and 78y varies. When the driving directions (poles) of the coils 79p and 79y are set so that the outputs from the position detecting elements 78p and 78y will be decreased (negative feedback), the lens holding frame 72 stabilizes at a position at which the outputs of the position detecting elements 78p and 78y are nearly zero by the driving force of the coils 79p and 79y.
Compensation circuits 728p and 728y are circuits for stabilizing the control system further, and driving circuits 719p and 719y are circuits for compensating for the applied current to the coils 79p and 79y. When command signals 730p and 730y are given from outside to the control circuit 94 from the control circuit (not shown), the lens holding frame 72 is driven very accurately by the command signals 730p and 730y.
FIG. 17 is a detailed view of the correction optical means drive control circuit 94 for driving the correction optical means, also illustrating only the control system for the pitch direction p (FIG. 16). The construction is the same for the yaw direction y.
In FIG. 17, current-voltage conversion amplifiers 732pa and 732pb amplify photo-current 731pa and 731pb which is generated in the position detecting element 78p when light enters from the light projecting element 76p to the position detecting element 78p, and a differential amplifier 733p determines the difference between the outputs of the current-voltage conversion amplifiers 732pa and 732pb. The difference between the outputs is proportional to the position of the lens holding frame 72 along the pitch direction p. The current-voltage conversion amplifiers 732pa and 732pb and the differential amplifier 733p correspond to the amplifier circuit 727p in FIG. 16.
A command amplifier 734p adds the command signal 730p to the output of the differential amplifier 733p and inputs the signal to a driving amplifier 735p. A driving circuit 729p in FIG. 16 is formed of a driving amplifier 735p, transistors 736pa and 736pb, and a resistor 737p. Resistors 738p and 739p, and a capacitor 740p constitute a known phase lead circuit corresponding to the compensation circuit 728p of FIG. 16.
An addition amplifier 741p determines the output sum (the total sum of the light received by the position detecting element 78p) of the current-voltage conversion amplifiers 732pa and 732pb and inputs the total sum to a light projection element driving amplifier 742p.
Since the light projecting element 76p is very susceptible to temperature or the like and the amount of light projection of the light projecting element 76p varies, the position detecting sensitivity of the differential amplifier 733p varies with the change in the amount of light projection. However, by driving the light projection element in accordance with the total sum of the light received by the position detecting element 78p as described above, i.e., by effecting control for maintaining the amount of light received at a constant level such that when the total sum of the light received is decreased, the amount of light emitted from the light projecting element 76p is increased, the position detection sensitivity change will be decreased.
In the above-described construction, the lock arm 721 which constitutes one member of the locking means 93 for locking and unlocking the lens holding frame 72 is turned about the screw 722 by means of the solenoid 719, and when a dowel 721a in the tip of the lens holding frame 72 is inserted into a hole 72d of the lens holding frame 72, the lens holding frame 72 will be locked.
A permanent magnet which is contained in the solenoid 719 and a movable iron core 719a which is connected to the lock arm 721 constantly attract each other. Therefore, when the lens holding frame 72 is locked, the locked state of the lens holding frame 72 is maintained even if no electric current is supplied to a coil (not shown) of the solenoid 719. When electric current is supplied to the coil of the solenoid 719 in a desired direction, the electromagnetic force of the coil cancels the attraction force of the permanent magnet, causing the force for urging the lock arm 721 toward the lock arm 721 to be weak. Since the lock arm 721 is urged by the spring 720 so as to be away from the lens holding frame 72, when the attraction force between the solenoid 719 and the movable iron core 719a becomes weak, the dowel 721a is pulled out of the hole 72d of the lens holding frame 72 by means of the force of the spring 720, causing the lens holding frame 72 to be unlocked. Since the attraction force between the solenoid 719 and the movable iron core 719a is not present even if the supply of electric current is stopped, the unlocked state of the lens holding frame 72 will be maintained by the urging force of the spring 720.
Next, when electric current is supplied to the coil of the solenoid 719 in an opposite direction, the solenoid 719 attracts the movable iron core 719a by the total force of the electromagnetic force and the attraction force of the permanent magnet. Thus, the urging force of the spring 720 is overcome, and the dowel 721a enters the hole 72d, causing the lens holding frame 72 to be locked.
As described above, electric current may also be supplied to the solenoid 719 only during a very short time as when the lens holding frame 72 is locked and unlocked, and the supply of electric current need not be continued more than that. Thus, the locking means 93 saves power.
The above-described optical apparatus of the prior art has the problems described below.
1 Maintaining the lens holding frame 72 in a locked or unlocked state is likely to be unstable.
2 Space efficiency is not good because the locking means 93 protrudes greatly outside the lens barrel 710.
3 Although the locking means 93 of the lens holding frame 72 has a function for locking and unlocking the lens holding frame 72, it does not have a function for restricting the movable range of the lens holding frame 72 when the lens holding frame 72 is unlocked, i.e., becomes ready for a correction operation.
The above problems will be explained below in more detail.
1 The operation for locking and unlocking the lens holding frame 72 is performed by a magnetic attraction force or a spring force. Therefore, when, for example, the lens holding frame 72 is maintained in an unlocked state, the movable iron core 719a is moved relative to the solenoid 719 by an inertial force due to disturbance vibration and the gap between the movable iron core 719a and the permanent magnet of the solenoid 719 becomes narrower, causing the magnetic attraction force to be larger than the spring force and resulting in the lens holding frame 72 being put in a locked state. If, on the contrary, disturbance vibration occurs when the lens holding frame 72 is maintained in a locked state, the lens holding frame 72 may be unlocked by the same phenomenon.
2 Although the solenoid 719 is compact and does not take a large amount of space, the lock arm 721 is long in the direction at right angles to the direction the movable iron core is moved. Therefore, the provision of a space along the length of the solenoid 719 and a space along the length of the lock arm 721 at right angles to the length of the solenoid 719 is necessary, and as a result, a large amount of space is taken. Further, since the locking means 93 is disposed outside the lens barrel, the total volume of the optical apparatus is large.
3 Although the locking means 93 has a function for locking and unlocking the lens holding frame 72, it does not have a function for restricting the movable range of the lens holding frame 72 when the locked state of the lens holding frame 72 is released. Therefore, a restricting means for making the lens holding frame 72 not move more than necessary is required.
When a photograph is taken by using the above-described optical apparatus having a shake prevention apparatus, if the optical apparatus is shaken by camera shake, the operation for eliminating the image blur due to the shake is performed as a result of the lens holding frame 72 being moved in the plane which intersects the optical axis. However, since the movement of the lens holding frame 72 has not been adjusted according to other variables which influence optical apparatus and the photographic conditions, in some cases, there is the risk that on the contrary the image blur correction operation might deteriorate the image quality even more. Therefore, to realize a shake prevention apparatus suited to the primary designed purpose of the optical apparatus such that it is desired to decrease the image deterioration on the image forming plane, it is necessary to restrict the amount of the movement of the lens holding frame 72 according to the situation in which the optical apparatus is used and the photographic conditions. Also, although the image blur is corrected as a result of the lens holding frame 72 performing the image blur correction operation, optical aberration occurs due to the movement of a correction lens 71 during the image blur correction operation, and the optical aberration causes the image to be deteriorated. Therefore, the balance between the image deterioration and the image blur prevention effect must be taken into consideration. Thus, means for restricting (adjusting) the amount of movement of the lens holding frame 72 is necessary.